This invention relates to an optical material useful as an optical element used for optical communication and a field of an optical information processing, particularly to an organic nonlinear optical material having a nonlinear optical effect and excellent in mechanical strength and molding property.
In order to apply laser beam to optical communication, optical information processing and optical processing, an optical element having various functions such as deflection, modulation or wavelength conversion. As such an optical element which assumes a role of the core, an optical material having a nonlinear effect has been known.
As the nonlinear optical material, research have been mainly carried out with respect to inorganic crystalline materials such as LiNbO.sub.3, LiIO, KH.sub.2 PO.sub.4 and GaAs.
However, these inorganic crystalline materials have involved the problem that a response more rapid than picosecond is difficult since an electron participating in chemical bonding between atoms or ions causes lattice vibration in response to light and also involved the problem that a breakage threshold level thereof to a strong laser beam is low and is MW/cm.sup.2 order. Also, these inorganic crystalline materials are generally used as a single crystal so that mechanical strength, particularly impact strength is a little whereby various defects such as bad mold processability are involved.
Also, as a nonlinear optical material, there have been known organic molecular crystalline materials such as urea, p-nitroaniline (p-NA) and 2-methyl-4-nitroaniline (MNA). These organic molecular crystalline materials have a large nonlinear optical effect caused by nonlocalized .pi. electron in the molecule and due to this electron polarization, they do not accept any effect from lattice vibration so that they show more rapid response and higher optical breakage threshold level than those of the inorganic crystalline materials.
These organic molecular crystalline materials are, however, also required to be a single crystal as in the inorganic crystalline materials in order to obtain a large nonlinear optical effect. Thus, those having high characteristics are insufficient in mechanical strength and thermal stability so that there involved drawbacks that their handling is extremely difficult and moldability is poor when molding them into, for example, an optical fiber or film.